Continuity mistake: When Buffy is shown pulling the secret chest out of her closet with weapons against the vampires, the window behind her shows daylight, but when she steps out of her window it is fully dark. There is also a cut scene right before that shows it was twilight, but there was late afternoon sunlight shining through the windows of her room. It's not possible for the sun to go down that fast.
Visible crew/equipment: When Buffy is going through the murdered Professor's office, Angel seems to trip through the doorway. To the top right above Angel's head a boom mike is visible twice.
Visible crew/equipment: When Buffy and Riley are talking at the crime scene, where he tells her about Maggie Walsh's death, one of the camera shots has a very visible black border around the entire edge of the screen as if the lens shade was visible in front of the lens and could be seen in the shot. (00:18:20 - 00:19:40)
Visible crew/equipment: After Buffy walks outside to hear the sirens, in the close up of Buffy's face on the upper right corner of the screen you can see a boom mike. (00:06:30)
Continuity mistake: In many historical flashbacks, most notably Spike's and Anya's, hair and wigs differ greatly from previous flashbacks or episodes. The director even discusses it during the commentary on Lies My Parents Told Me, saying that he doesn't understand why the wigs aren't consistent.
Blood Ties - S5-E13
Continuity mistake: In the first scene of the episode, just after the teaser, the Scoobies are gathered around the table at Giles' magic shop. During the second part of the scene, we can see Anya is alternatively lying her arms under or above the table depending on the camera angle, whether from behind or facing her. (00:01:55 - 00:03:15)
Continuity mistake: When Spike is stalking Buffy in front of her house, she somehow senses him and pulls him out of behind the tree in front of her porch. While he is being pulled out, he has no cigarette in his mouth. However in the next close-up shot, he has one (which he then quickly throws away). (00:29:55)
Visible crew/equipment: In the final scene where Buffy apologizes to Dawn, a microphone is visible in the upper left corner, from the camera angle behind Dawn, just after she says "you hurt my arm." (00:40:00)
Visible crew/equipment: When Riley goes to Spike's crypt to ask him for information about Dracula, the microphone appears in the upper right hand corner of the screen. (00:17:55)
Continuity mistake: When Xander is shot by the demon's lightning rod, he falls on a heap of black trash bags. When he is helped to stand up, different bags, pink and white ones, are visible instead. (00:11:30)
Continuity mistake: When the group is debriefing about their first Dracula encounter at Giles', Anya is sitting on the sofa with her hands crossed on her lap. In the next shot she has her arms straight with the palms of her hands on the sofa cushion, fingers towards the back. (00:11:25)
Visible crew/equipment: In the scene where Spike escapes from The Initiative a black curtain can be seen to the right of the screen after the other vampire is release from his cell. The curtain serves no purpose to the set or scene and it disappears in the next shot. (00:13:25)
Homecoming - S3-E5
Visible crew/equipment: When Buffy and Faith are in the library, a person's arm wearing a white shirt can be seen on the left side of the screen behind Buffy in one shot.
The Freshman - S4-E1
Continuity mistake: When Buffy is talking to Giles after his run, his towel moves from being on one shoulder to being across his back and over the other shoulder to being back on one shoulder.
Visible crew/equipment: When Giles picks Buffy up in his car, you can see lighting and camera equipment on the right.
Where The Wild Things Are - S4-E18
Visible crew/equipment: In the scene where Xander and Anya make the last attempt to rescue Buffy and Riley, Anya is attacked by some vines and you can see another set of hands from the crew pushing the vine towards her.
Where The Wild Things Are - S4-E18
Visible crew/equipment: Toward the end of the episode Giles, Tara and Willow contact the spirits. Just after the spirits vanish, in the bottom left corner of the screen a crew member's leg is visible.
Continuity mistake: Near the end, when Spike takes the cup of blood from the fridge, we can see that it is full to within a 1/4 inch of the rim. However, when the shot changes and he drinks it, he tips the cup almost 45 degrees before putting his lips to the cup and drinking. If the cup had been as full as previously shown, the blood would have begun pouring out long before Spike ever drank form it.
Chosen answer: He had larangitis and because of the shooting specifications they had to have him shoot the scene with a bad throat, they then re-recorded his lines and dubbed them. At various points during the scene and indeed the episode you can see him touch his throat or rub it.